I am not sure if you're implying that that's why a 'French Metirc Thread' is likely to be correct or if you're saying 'It's French, it's bound to be odd'. Having maintained Citroen car for 13 years, I came to the conclusion that French engineering is often strange, but equally it's often very good (and ingenious). This telephone is a case in point. When I started work on it, I noticed that there appeared to be no anti-sidetone indcution coil in the unit, and that only 2 wires of the handset cable went wanywhere inside the base of the tleephone. After some more investigation I realised that the earpiece insert has 3 connections, and aftrer carefully dismantling it (I machined off the rolled-over lip that held the front cover on, then removed that and the diaphragm -- the whole thign is held together by the screw-on plastic cap when the handset is assembled), I discovered that the earpiece sinding is tapped, and that thaere's a resistor inside the earpiece too. This forms an anti-sidetone circuit from the looks of things. As I dad, French engineering is odd, but good :-) That I can well believe. The only place I could find mention of it was in an old Machineries Handbook. None of my other sets of workshop tables cover it. What makes this a little odd is that the tap and die for this thread are not difficult to find. If nobody uses it any more, why are the cutting tools still made... Yes, I am coming round to that view :-). -tony